Flexible positive temperature coefficient sheet and method for making the same

Abstract

A flexible sheet of positive temperature coefficient (PTC) material formed of a polymer resin and a conductive filler, the sheet of PTC material having a thickness in a range of 10 μm to 100 μm. A method for forming the flexible sheet of positive temperature coefficient material may include preparing a PTC ink from a polymer resin, a conductive filler, and a solvent, applying the PTC ink to a substrate, pulling a blade over the PTC ink to create a uniformly thick layer of the PTC ink on the substrate, and allowing the PTC ink to dry so that the solvent evaporates and leaves a solid layer of PTC material on the substrate.

We claim: 
     
       1. A flexible sheet comprising a layer of positive temperature coefficient (PTC) material formed of a polymer resin, an anti-arcing material, and a conductive filler, the layer of PTC material having a thickness in a range of 10 μm to 100 μm, a plurality of perforations defining a plurality of openings in the layer of PTC material, wherein greater than 25% of the layer of PTC material is open space defined by the openings. 
     
     
       2. The flexible sheet of  claim 1 , wherein greater than 50% of the layer of PTC material is open space defined by the openings. 
     
     
       3. The flexible sheet of  claim 2 , wherein greater than 75% of the layer of PTC material is open space defined by the openings. 
     
     
       4. The flexible sheet of  claim 1 , wherein the thickness of the layer of PTC material is in a range of 15 μm to 25 μm. 
     
     
       5. A method for forming a flexible sheet of positive temperature coefficient (PTC) material, the method comprising:
 preparing a PTC ink from a polymer resin, an anti-arcing material, a conductive filler, and a solvent; 
 applying the PTC ink to a substrate; 
 allowing the PTC ink to dry so that the solvent evaporates and leaves a solid layer of PTC material on the substrate; and 
 perforating the solid layer of PTC material such that greater than 25% of the solid layer of PTC material is open space defined by the openings. 
 
     
     
       6. The method of  claim 5 , further comprising pulling a blade over the PTC ink to create a uniformly thick layer of the PTC ink on the substrate. 
     
     
       7. The method of  claim 6 , wherein the uniformly thick layer of the PTC ink has a thickness in a range of 10 μm to 100 μm. 
     
     
       8. The method of  claim 7 , wherein the thickness of the uniformly thick layer of the PTC ink is in a range of 15 μm to 25 μm. 
     
     
       9. The method of  claim 5 , further comprising adding at least one of an antioxidant and an adhesion promoter to the PTC ink. 
     
     
       10. The method of  claim 5 , wherein the polymer resin is formed of semi-crystalline polymers including at least one of polyvinylidene difluoride, polyethylene, ethylene tetrafluoroethylene, ethylene-vinyl acetate, and ethylene butyl acrylate. 
     
     
       11. The method of  claim 5 , wherein the conductive filler is formed of at least one of tungsten carbide, nickel, and titanium carbide. 
     
     
       12. An electronic device comprising:
 a protected component; and 
 a flexible positive temperature coefficient (PTC) device including a flexible sheet of PTC material formed of a polymer resin, an anti-arcing material, and a conductive filler, the flexible sheet of PTC material coupled to an exterior surface of the protected component, the flexible PTC device electrically connected to the protected component and adapted to arrest or mitigate electrical current flowing through the protected component, a plurality of perforations defining a plurality of openings in the flexible sheet of PTC material, wherein greater than 25% of the flexible sheet of PTC material is open space defined by the openings. 
 
     
     
       13. The electronic device of  claim 12 , wherein the flexible sheet of PTC material has a thickness in a range of 10 μm to 100 μm. 
     
     
       14. The electronic device of  claim 12 , wherein the flexible sheet of PTC material covers greater than 25% of the exterior surface of the protected component. 
     
     
       15. The electronic device of  claim 14 , wherein the flexible sheet of PTC material covers greater than 50% of the exterior surface of the protected component. 
     
     
       16. The electronic device of  claim 15 , wherein the flexible sheet of PTC material covers greater than 75% of the exterior surface of the protected component. 
     
     
       17. The electronic device of  claim 12 , wherein the protected component comprises at least one battery, and wherein the flexible PTC device is connected electrically in series between the at least one battery and an electrical load.